Just here on Upverter there is a great material to learn hardware design (as well as steps to start designing on Upverter). It goes through everything from Ideation (the start of an idea) to production.

In terms of books Designing Embedded Hardware is a good introduction to embedding computer systems in everything for phones to refrigerators. It won't make you an expert per say but is a good starting point for a total beginner.

I am actually starting to dive into both, I think two materials are great to learn in unison. I am looking to get into hardware myself. We are in exciting times for getting into hardware thanks to platforms like Upverter that enable us to have an easier time creating and collaborating on hardware design and Kickstarter that gives cool ideas a market to receive funding.